Tesla uses lots of GPUs for training autopilot, I would be surprised if they wouldn’t have people writing optimized shaders for some of the tasks.
This operation is not just interviewing people, it’s a kind of knowledge transfer and finding the people who are the best at explaining how the code works and can answer deep technical questions. This is how Elon works generally (if you look at the SpaceX interview, you can see that he just goes to people and asks them questions about the parts of the rocket while he’s doing the interview).